Articles such as disposable absorbent garments have numerous applications including diapers, training pants, feminine care products, and adult incontinence products. A typical disposable absorbent garment is formed as a composite structure including an absorbent assembly disposed between a liquid permeable bodyside liner and a liquid impermeable outer cover. These components can be combined with other materials and features such as elastic materials and containment structures to form a product which is specifically suited to its intended purposes.
Absorbent garments may be formed from woven webs of material, or non-woven webs of material, or combinations thereof. In particular, a non-woven web is a web having a structure of individual fibers or threads which are interlaid, but not in a regular or identifiable manner as in a knitted or woven fabric. The term also includes individual filaments and strands, yarns or tows as well as foams and films that have been fibrillated, apertured, or otherwise treated to impart fabric-like properties. Non-woven fabrics or webs have been formed from many processes such as for example, meltblowing processes, spunbonding processes, and bonded carded web processes.
In order to avoid defects when forming diapers, and other absorbent garments from web material, it is important that the web strain be controlled during the manufacturing process. Changes in the speed of the web material within a fixed span and/or changes in the physical properties of the web material can result in elongation of a web material held at a constant tension. Defective absorbent garments can result from such elongation because it effects the relative placement product components on the web. One method of controlling web strain involves monitoring and controlling web tension during manufacturing. However, this method often proves inadequate in controlling strain variability. As a result, manufacturing tolerances can widen.
In spite of past efforts, there is a need for improved methods and systems for controlling web strain variability during a manufacturing process. There is a need for systems and methods that permit monitoring and controlling web strain during manufacturing.
The invention described below addresses one or more of these and other disadvantages and needs.